A reentry is a spacecraft with humans or stardust coming from space and landing on Earth (or on Mars). It is physically impossible.

But you totally fail at demonstrating that "It is physically impossible."! You just ridicule everything without presenting reasons!

These just so much total rubbish that it would take ages to unravel it all and then you'd ignore it anyway so why bother.

But you do say:

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Delta-v = ve ln (m0/m1)ESAmple 1 - you want to slow down a 6.000 kg (m0) three parts Soyuz module entering the atmosphere backwards at a almost horisontal speed of 8.000 m/s (no influence of gravity). You have only, say 2.000 kg of fuel aboard and it is ejected at a velocity ve of, say 2.800 m/s. m1 = 4.000 kg. Delta-v is only 1.135 m/s! After burning all fuel your speed will be 6.865 m/s - still flying backwards.

But this is irrelevant tripe because in an atmospheric reentry braking to sub-sonic speeds is by atmospheric drag NOT rocket thrust!Landing on the Moon with no atmosphere does need a powered descent but landing on earth means that can be avoided. Have you read this yet? 4.1.7 Returning from Space (PDF).

Then you say:

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To return to Earth the Shuttle must evidently slow down a lot after undocking. Or speed up? How can it be done?

No, "the Shuttle" does NOT need to "slow down a lot after undocking" to start the reentry. For the ISS at 280 km with an orbital speed of 7737 m/s needs a de-orbit burn Delta-V of only about 47 m/s to bring it down to 120 km.And at 460 km with an orbital speed of 7635 m/s needs a de-orbit burn Delta-V of only about 98 m/s to bring it down to 120 km.Hence little propellant is needed and the Space Shuttle used the OMS engines for this.

To return to Earth the Shuttle must evidently slow down a lot after undocking. Or speed up? How can it be done?

No, "the Shuttle" does NOT need to "slow down a lot after undocking" to start the reentry. For the ISS at 280 km with an orbital speed of 7737 m/s needs a de-orbit burn Delta-V of only about 47 m/s to bring it down to 120 km.And at 460 km with an orbital speed of 7635 m/s needs a de-orbit burn Delta-V of only about 98 m/s to bring it down to 120 km.Hence little propellant is needed and the Space Shuttle used the OMS engines for this.

On reaching the perigee in half an orbital period the Shuttle starts atmospheric braking.That perigee altitude can be adjusted to control the reentry angle.

I may or may not waste more time on this but who cares? You won't take the slightest bit of notice!

Well, if your spacecraft orbits Earth at 7 635 m/s leaving the ISS at 450 000 m altitude it needs a lot braking to start re-entry at 120 000 m/altitude. Coming back from the Moon you velocity at 120 000 m altitude is >11 000 m/s when starting re-entry ... and it is pretty fast. As soon as you contact the Earth atmosphere, you start to heat up and ... burn up. There is nothing left of you.It is one reason why nobody wins my Challenge.

Coming back from the Moon you velocity at 120 000 m altitude is >11 000 m/s when starting re-entry ... and it is pretty fast. As soon as you contact the Earth atmosphere, you start to heat up and ... burn up. There is nothing left of you.

Suppose the spacecraft is orbiting at an altitude of 450 km with an orbital velocity of 7640 m/s and the reentry altitude is at an altitude of 120 km with the required entry angle.

All that needs be done is to reduce the velocity enough to enter an elliptical orbit (another Hohmann transfer orbit) with the perigee enough below that 120 km to get the right entry angle. I'm not going to attempt to calculate exactly what that perigee need be - I'll "guess" and put that perigee at 80 km.

The velocity needs to be reduced by only 107 m/s to 7533 m/s a the apogee for a perigee of 80 km.If there were no air drag, after half an orbit, in 45 minutes the spacecraft would be down to the 80 km and travelling at 7965 m/s but air drag starts before then.

Sometime before reaching the reentry interface any unwanted fuel and modules not needed (eg the Soyuz equipment module) are disposed of to burn un on there own.

But the point is it takes very little reduction in velocity to start the deorbit manoeuvre.

This is not an ideal diagram but it might illustrate this process:Not that the spacecraft is orbiting clockwise in it.The "landing burn" would only be needed if the atmosphere were not dense enough for a complete atmospheric reentry (eg on the Moon, minor planets, asteroids and possibly on Mars). On Earth an atmospheric reentry can slow the craft to where parachutes can be deployed - this is even done on Mars with two stage parachutes.

Quote from: Heiwa

Coming back from the Moon you velocity at 120 000 m altitude is >11 000 m/s when starting re-entry ... and it is pretty fast.

Sure, you are travelling very fast!

Quote from: Heiwa

As soon as you contact the Earth atmosphere, you start to heat up and ... burn up.

Sure, you start to heat up!But a properly designed and oriented heat shield will cause most of the kinetic energy to be expended in heating the air to plasma temperatures and not the reentering module.

Quote from: Heiwa

There is nothing left of you.

Incorrect! You simply say these things with no evidence to back your claim - present the evidence or run away!If you have a "properly designed and oriented heat shield" most of the energy ends up heating the atmosphere.

As soon as you contact the Earth atmosphere, you start to heat up and ... burn up.

Sure, you start to heat up!But a properly designed and oriented heat shield will cause most of the kinetic energy to be expended in heating the air to plasma temperatures and not the reentering module.

Quote from: Heiwa

There is nothing left of you.

Incorrect! You simply say these things with no evidence to back your claim - present the evidence or run away!If you have a "properly designed and oriented heat shield" most of the energy ends up heating the atmosphere.

According my information any "heat shield" just heats up and is ripped apart in contact with the atmosphere. It means that the spacecraft also is destroyed.To win my Challenge you have to have a robust heat shield.

As soon as you contact the Earth atmosphere, you start to heat up and ... burn up.

Sure, you start to heat up!But a properly designed and oriented heat shield will cause most of the kinetic energy to be expended in heating the air to plasma temperatures and not the reentering module.

Quote from: Heiwa

There is nothing left of you.

Incorrect! You simply say these things with no evidence to back your claim - present the evidence or run away!If you have a "properly designed and oriented heat shield" most of the energy ends up heating the atmosphere.

According my information any "heat shield" just heats up and is ripped apart in contact with the atmosphere. It means that the spacecraft also is destroyed.

Please post the source of your information just so that we can check that is didn't come from the posterior of a male bos taurus or was dreamed up after dining on Psilocybe cubensis.

As soon as you contact the Earth atmosphere, you start to heat up and ... burn up.

Sure, you start to heat up!But a properly designed and oriented heat shield will cause most of the kinetic energy to be expended in heating the air to plasma temperatures and not the reentering module.

Quote from: Heiwa

There is nothing left of you.

Incorrect! You simply say these things with no evidence to back your claim - present the evidence or run away!If you have a "properly designed and oriented heat shield" most of the energy ends up heating the atmosphere.

According my information any "heat shield" just heats up and is ripped apart in contact with the atmosphere. It means that the spacecraft also is destroyed.

Please post the source of your information just so that we can check that is didn't come from the posterior of a male bos taurus or was dreamed up after dining on Psilocybe cubensis.

Easy, I have contacted known 'heat shield' builders about delivery, price and guarantee that it works but ... no offers received. It seems all info about such 'heat shields' are military secrets due to US national security and US anti-terrorism reasons.Pls help me to find a good 'heat shield' manufacturer and we can discuss.

Any sensible business would see any of the above and decide that the safest thing to do is ignore the request!

Quote from: Heiwa

It seems all info about such 'heat shields' are military secrets due to US national security and US anti-terrorism reasons.

Rubbish!The only 'heat shields' that might be "military secrets due to US national security and US anti-terrorism" would be those fro ICBMs etc and I'm certain any nation capable of building an ICBM would have no problem designing suitable heat shields.

Quote from: Heiwa

Pls help me to find a good 'heat shield' manufacturer and we can discuss.

In other words, you are making up more fairy stories.

Now quote your sources for your claim that "any 'heat shield' just heats up and is ripped apart in contact with the atmosphere" without any more fabricated crap.

Easy, I have contacted known 'heat shield' builders about delivery, price and guarantee that it works but ... no offers received.

Did you provide detailed specifications of your reentry vehicle and reentry procedures so that they could recommend the best heat shield product for your needs?

Of course.

What were the specifications you sent and to whom?

Simple - the 'heat shield' should protect my spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s, so it doesn't melt, before I open a parachute at 50 m/s speed for a soft laning. I asked the usual NASA, SpaceX manufacturers.No replies!

Simple - the shield should protect my spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s, so it doesn't melt before a open the parachute at 50 m/s speed. I asked the usual NASA, SpaceX manufacturers.No replies!

As I said before, one look at your credentials and they wouldn't touch your request with a barge-pole!

But who, may I ask, were the manufacturers of the heat shields used on by NASA and SpaceX?

And if you simply said "the shield should protect your spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s" they would instantly know that you didn't know what you were talking about.

Simple - the shield should protect my spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s, so it doesn't melt before a open the parachute at 50 m/s speed. I asked the usual NASA, SpaceX manufacturers.No replies!

As I said before, one look at your credentials and they wouldn't touch your request with a barge-pole!

But who, may I ask, were the manufacturers of the heat shields used on by NASA and SpaceX?

And if you simply said "the shield should protect your spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s" they would instantly know that you didn't know what you were talking about.

Only way to go from the Moon to the Earth is to take off from the Moon and then, when free of Moon gravity, drop down back on Earth due to Earth gravity NASA/Apollo style 1969/72. A heat shield then protected the Apollo spacecraft through the atmosphere on the last bit and also acted as a brake (!!!) before a parachute was used for a soft landing.

There is no other way! NASA and SpaceX apparently make their own heat shields, so I asked them.

Easy, I have contacted known 'heat shield' builders about delivery, price and guarantee that it works but ... no offers received.

Did you provide detailed specifications of your reentry vehicle and reentry procedures so that they could recommend the best heat shield product for your needs?

Of course.

What were the specifications you sent and to whom?

Simple - the 'heat shield' should protect my spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s, so it doesn't melt, before I open a parachute at 50 m/s speed for a soft laning. I asked the usual NASA, SpaceX manufacturers.No replies!

Hmmm... It seems that we have different ideas of what "detailed specifications" and "reentry procedures" mean.

Simple - the shield should protect my spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s, so it doesn't melt before a open the parachute at 50 m/s speed. I asked the usual NASA, SpaceX manufacturers.No replies!

As I said before, one look at your credentials and they wouldn't touch your request with a barge-pole!

But who, may I ask, were the manufacturers of the heat shields used on by NASA and SpaceX?

And if you simply said "the shield should protect your spacecraft dropping down from the Moon through Earth atmosphere at speed 11 000 m/s" they would instantly know that you didn't know what you were talking about.

Only way to go from the Moon to the Earth is to take off from the Moon and then, when free of Moon gravity, drop down back on Earth due to Earth gravity NASA/Apollo style 1969/72.

The Apollo Spacecraft did not "drop down back on Earth" but returned from the Moon on a transfer orbit.This might indicate the trajectories (You can click this and see the full-sized image):

And here is the reentry and landing phase. You could hardly call that "dropping down back on Earth due to Earth gravity" (again click image to enlarge it - twice for maximum size).

Quote from: Heiwa

A heat shield then protected the Apollo spacecraft through the atmosphere on the last bit and also acted as a brake (!!!) before a parachute was used for a soft landing.

There is no other way!

Quote from: Heiwa

Well, there is a powered landing as on the moon but they saved the fuel by using an atmospheric reentry.

NASA and SpaceX apparently make their own heat shields, so I asked them.

No, NASA did not make the heat shields for either the Apollo or the Orion command modules.

If you had made such requests you would have known that the didn't so frankly I do not believe you.

Can this thread be locked now that heiwa has proven to be an absolute piece of shit.

Yes we have known he is a disgusting pathetic liar who has nothing and done nothing... But this is the internet, plenty of people like that unfortunately... His last most recent comments show how over the line disgusting he is.

This thread has already proven how much of a lie it is.

Heiwa doesn't have the money, the challenge is real and he is a pathetic joke. Threads have ended for much much less.

So stop giving this pile of garbage ANYTHING he deserves NOTHING! Especially a thread that is stickied. Mods, do your job for this site